Uniform basis weight fibrous structures, even textured and/or embossed fibrous structures, comprising a plurality of filaments and solid additives, for example fibers, are known in the art. However, such known fibrous structures do not comprise two regions that exhibit at least one common micro-CT intensive property, such as basis weight, that differs in value, wherein the common micro-CT intensive property transitions between the two regions.
Known uniform basis weight fibrous structures comprising a plurality of filaments and solid additives, for example fibers, such as pulp fibers, do not comprise two regions that exhibit at least one common micro-CT intensive property that differs in value, wherein the common micro-CT intensive property transitions (changes in value along a distance between two points within the two regions) between the two regions. In other words, regions of uniform basis weight fibrous structures, exhibits the same or substantially the same common micro-CT intensive property value along a distance between two points within the fibrous structure.
Prior Art FIG. 1 shows an example of a known method 100 for making a known uniform basis weight fibrous structure 10 comprising a plurality of filaments and solid additives. This known method 100 fails to create a fibrous structure 10 comprising two regions that exhibit at least one common micro-CT intensive property, such as micro-CT basis weight, that differs in value, wherein the common micro-CT intensive property transitions between the two regions. As shown in Prior Art FIG. 1, the method 100 comprises the step of mixing a plurality of filaments 12 with a plurality of solid additives 14. In one example, the solid additives 14 are wood pulp fibers, such as SSK fibers and/or Eucalyptus fibers, and the filaments 12 are polypropylene filaments. The solid additives 14 may be combined with the filaments 12, such as by being delivered to a stream of filaments 12 from a hammermill 66 via a solid additive spreader 67 to form a mixture of filaments 12 and solid additives 14. The filaments 12 may be created by meltblowing from a meltblow die 68. The mixture of solid additives 14 and filaments 12 are collected on a collection device, such as a belt 70 to form a fibrous structure 10. A forming vacuum 17 aids in the collection of the solid additives 14 and filaments 12 onto the collection device, by pulling air through the collection device. The amount of vacuum from the forming vacuum 17 was sufficient to collect the solid additives 14 and filaments 12 onto the collection device. The resulting fibrous structure 10 has uniform basis weight properties.
Fibrous structures made by a method as described in Prior Art FIG. 1 have uniform distribution of a plurality of filaments and solid additives which therefore renders the fibrous structure restricted to deliver an overall performance level characteristic of the fibrous structure possessing such uniform, overall composition of the plurality of filaments and solid additives. In other words, a fibrous structure exhibiting a uniform plurality of filaments and solid additives, results in the fibrous structure exhibiting the same performance and properties across the entire fibrous structure.
The performance of a fibrous structure as measured by its strength, burst, flexibility, absorbency, and/or visual aesthetics properties may be a function of its microstructure as measured by intensive properties such as basis weight, thickness, density, bonding, etc. The overall performance of a fibrous structure may be increased by creating regions within the structure where intensive properties including basis weight, thickness, density, bonding, and combinations thereof, are transformed or made to be different so as to have a region delivering high levels of one performance attribute in one region and then high levels of another performance attribute in another. Having different regions with differing high levels of performance in one fibrous structure yields overall performance levels superior to a uniform or no region fibrous structure. For example, the overall performance of the fibrous structure may be maximized by having regions within the fibrous structure which are responsible for delivering one performance requirement such as strength, while a separate region delivers a separate performance requirement such as absorbency or visual aesthetics.
The delivery of overall fibrous structure performance within a region is directly related to the intensive properties imparted to the regions and most importantly, the intensive property transition rate or slope between the regions. The intensive property transition reflects the rate of change in an intensive property between one region and an adjacent region. More specifically, the intensive property transition is the slope, the rate of change, or ratio of the intensive property difference between one region and another region in a numerator with the fibrous structure distance over which the change occurs appearing in the denominator. Such a transition or slope value may influence the performance of the fibrous structure as for example, high transitions or slopes conveys sharp and distinctive visual aesthetics or greater ability to scoop up particulate in a cleaning situation.
Therefore, a problem that has not been addressed by known fibrous structures comprising a plurality of filaments and a plurality of solid additives, such as fibers, is the creation of fibrous structures that comprise two regions that exhibit at least one common micro-CT intensive property that differs in value, wherein the common micro-CT intensive property transitions between the two regions.
In light of the foregoing, there is a need for a fibrous structure that comprises two regions that exhibit at least one common micro-CT intensive property that differs in value, wherein the common micro-CT intensive property transitions between the two regions that overcome the negatives of the known fibrous structures without such regions and methods for making such fibrous structures.